1. Field of the Invention
The present invention relates to a composite display apparatus incorporating an image pickup optical system for taking in light from image information of the outside to form an image thereof on an image pickup device and a display optical system for permitting an observer to observe the image information displayed on a display device such as a liquid crystal panel or the like, which is constructed in compact size as a whole, and, more particularly, to such apparatus suitably applicable to devices called head-mounted displays and goggle-type displays.
2. Related Background Art
The devices suggested heretofore include a device constructed in such structure that a compact CCD camera is mounted on a head-mounted display (HMD) and image information obtained from the compact CCD camera is displayed in the HMD as it is or a device constructed in such structure that the image information obtained from the compact CCD camera is processed and converted into some image information and the image information thus converted is displayed in the HMD. In addition, there are also a variety of suggestions about a seethrough HMD (the HMD having structure for permitting the light from the outside to be observed directly at the angular magnification 1) as a type of the HMD.
The HMD of this type will suffer parallax if the eye-ball optical axis of the display optical system for observing the image information displayed on the display device of the HMD is offset against the optical axis of the CCD camera for imaging the image information of the outside on the CCD surface. The devices having both the image pickup optical system and the display optical system without the parallax are suggested, for example, in Japanese Laid-open Patent Applications No. 4-22358 and No. 5-303053.
In the display optical system suggested in Japanese Laid-open Patent Application No. 4-22358, light emitted from a compact liquid crystal panel is guided via a flat half mirror and thereafter to the eye by an eyepiece. On the other hand, the image pickup optical system is arranged so that the light from the outside is guided via a flat half mirror and thereafter is focused on a compact camera. Since this flat half mirror was mounted at 45.degree., the scale of the apparatus tended to become large. In addition, the seethrough optical system was unable to be established, because there was the eyepiece in front of the eye.
Japanese Laid-open Patent Application No. 5-303053 discloses the structure that permits the seethrough optical system to be established, but the optical system was complex and the apparatus tended to become very large.
Further, in cases where a reflective liquid crystal panel was used as a display element, a separate illumination optical system had to be mounted and thus the scale of the overall apparatus tended to become large.
With the image observing apparatus including the HMDs and the like, a significant challenge is to decrease the scale and weight of the overall apparatus, because the apparatus is mounted on the head of the observer. There are also desires for compact apparatus having no parallax and permitting establishment of the seethrough optical system.